1. Field of the Invention
The present invention relates to a fan structure with improved waterproof properties designed for applications where sucked air contains water, and a battery pack using this fan structure.
2. Description of the Related Art
A battery pack consists of a battery assembly made of a plurality of rechargeable batteries and a charge/discharge control unit. To prevent a decrease in power output or battery life due to the heat that accompanies the charge and discharge of the batteries, some battery packs include cooling passages between adjacent batteries and a fan for supplying and discharging a cooling fluid to and from the cooling passages via supply and discharge passages.
A battery pack 41 shown in FIG. 7, for example, consists of a battery unit 45, a charge/discharge control unit 48 arranged on one side of the battery unit 45, and a fan unit 49 arranged on the other side of the battery unit 45, these units being accommodated in an outer case 50. The battery unit 45 includes a battery assembly 42, which consists of a plurality of parallel arranged rechargeable batteries 43 with cooling passages formed therebetween, a supply passage 46 above the batteries for feeding cooling air, and a discharge passage 47 below the batteries for discharging the cooling air.
At one end in the upper part of the fan unit 49 is opened an outside air inlet 51a, which connects to an outside air introducing passage 51 that communicates with the supply passage 46 at the opposite end from the air inlet. A fan 52 is arranged below, and a connection duct 54 is provided for connecting an inlet 53 opened in the lower face of the fan 52 with the discharge passage 47.
FIG. 8 shows the fan 52 in more detail. A base plate 55 is arranged at the top, and a motor 57 and a circuit substrate 56 for controlling the motor are mounted to the lower face of the base plate 55. A bladed wheel 59 is secured to the output shaft 58 of the motor 57. A fan case 60 or scroll housing encases these circuit substrate 56, motor 57, and bladed wheel 59. The open end 60a at the top of the fan case 60 is secured to the base plate 55. The inlet 53 is coaxial with the bladed wheel 59 and opened in the lower face of the fan case 60. The outlet 61 of the fan case 60 is connected to an exhaust duct outside the battery pack 41.
Operating the motor 57 of the fan 52 introduces cooling air from the outside air inlet 51a, which passes through the supply passage 46 and cooling passages for heat exchange with the rechargeable batteries 43. After cooling the batteries 43, the air is sucked through the discharge passage 47 into the inlet 53 of the fan 52, expelled from the outlet 61 by the pumping action of the bladed wheel 59 and scroll housing, and exhausted to the outside through an exhaust duct. A temperature rise of the rechargeable batteries 43 is thus prevented.
Japanese Utility Model Laid-Open Publication No. 55-112100 shows a waterproof structure of an electric fan used for cooling a condenser or the like of a car cooler. To protect the output shaft bearing from water or mud, cylindrical waterproof walls extend from the fan secured to the output shaft of the motor to the end face and to the outside of the motor, and disc-like waterproof barriers extend radially from both end faces of the motor, whereby labyrinths are formed in the path from outside to the bearing of the output shaft.
The fan 52 shown in FIG. 8 is reduced in size in the up and down directions because of the design wherein the circuit substrate 56 is arranged between the base plate 55 and the motor 57. It is therefore suitable for an application with space limitations such as a battery pack mounted on a vehicle. On the other hand, when the driver drives the car along a coast road, for example, at a stormy or windy time, the cooling air introduced from the inlet 53 may contain seawater mist. Also, the cooling air may contain moisture or dust if the car is driven under harsh environments. In such cases, because the circuit substrate 56 is exposed to the cooling air currents, there is a danger that short-circuiting or other malfunctions may occur due to salt, water, or dust adhered to the circuit substrate 56.
The waterproof structure shown in Japanese Utility Model Laid-Open Publication No. 55-112100 is a structure which consists of labyrinths formed in the path from outside to the output shaft bearing to prevent entrance of water or the like into the output shaft bearing, and not applicable to the fan shown in FIG. 8.